The proposed research continues the characterization of a simple sequence DNA, repeated (C-C-C-C-A-A),that is interspersed in both macronuclear and micronuclear chromosomal DNA in the ciliated protozoan Tetrahymena. This DNA sequence, also found at the termini of the extrachromosomal rDNA in the macronucleus, is implicated in DNA sequence rearrangements occurring during macronuclear differentiation. This DNA is packaged in chromatin in a form different from nucleosomes in the macronucleus; the situation in the micronucleus is being investigated. The DNA and its structurally associated protein(s) will be purified and the protein(s) characterized. Using recombinant DNA methods, repeated (C-C-C-C-A-A) DNA from the micronucleus will be cloned for use in filter binding assays in a search for proteins that bind this DNA sequence selectively. Such binding proteins will be sought from conjugating cells undergoing macronuclear differentiation. DNA-cellulose or DNA-sepharose columns will be prepared from this DNA. In addition, models for the role of this DNA sequence in macronuclear differentiation will be tested using cloned Tetrahymena cells of defined genetic background.